Halo 2 (2004)

Halo 2 takes place after the events of Halo: Combat Evolved. (Obviously) The Chief returns to Earth only to find it under attack. The Covenant has also found the Dreadnaught, an ancient Forerunner battle ship. The Prophet of Truth (the Covenant's leader) launched this attack planning to wipe out the human race. Halo 2 also features a new character, the Arbiter who has a dark and twisted past. he becomes the best soldier in the Covenant empire.

This game also features increased graphics, voice acting, NPCs, and weapons. (Non Player Characters)

Halo: Combat Evolved (2001)

Halo: Combat Evolved is the Master Chief's first step to nerdy stardom. The first Halo game takes place after Halo Reach (2010). While escaping the doomed planet of Reach, Captain Keyes,The Chief, Sergeant Johnson, and a small army of UNSC Marines crash land The Pillar of Autumn into the Halo named Installation 04. There the Chief fights thousands of Covenant soldiers and learns the secrets that Halo possesses, the Flood.

The Master Chief

He's traveled near and far to protect the human race from annihilation. He faught the Covenant,the Flood, and even his ancient ancestors, the Forerunners. With his trusty AI companion ,Cortana, the Master Chief can do anything. Even destroy the ancient Halos.

From Halo: Combat Evolved, the Chief has fought his way through millions of Covenant hordes, survived throught flood outbreaks, and prevented the entire galaxy from being destroyed.

The Chief,who's real name is John- Spartan number 117, is a bio-enhanced super human. he was abducted in 2527, when he was only 6, by the UNSC. their plan was to create these soldiers and stop the rebel insurecctionists. That was before the Covenant arrived. Unprovoked, the Covenant declared war on the entire human species. Hundreds of worlds were destroyed, or glassed, and billions were killed.